I updated my MacBook Pro and now when i login in it shuts down by it's self

This morning I did a Software update on my Mac Book Pro (Security Update 2015-003 1.0), I saw the progress bar for it's installation and shortly after my laptop restarted. I typed in my password and the progress bar appeared on my screen - it loaded to about 30% before it froze for 20 minutes; I shut it off and tried to restart. But this time the progress bar loaded to 50% and then it froze so once again I waited and then pressed the power button. I waited a few hours before turning it on again, i typed my password, the progress screen appeared for about a minute as it loaded to about 40% and then it shut off. I tried it twice and the same things happen. I do not have a backup and am worried of losing data.

PS: Just to add i tried to go in to "Safe Mode" by rebooting the laptop as many of the other posts have suggested, but to no luck it just didn't work.